Electromagnet for telegraphones.



' no... PB-DERSEN & v. PoULsEN.v

ELEGTROMAGET FOB TELEGBAPHONES. APPLIOAkT/IQN FILED APB. 9,1902.

l9,304. h Patented oct.6,19o8.

5y-fr Y EW.

E UNITED STATES PATENT OFFICE.

PEDER OLF PEVDERSN AND VALDEMAR POULSEN, OF OPENHAGEN, DENMARK, ASSIGN- ORS TO AMERICAN TELEGRAPHONE COMPANY, A CORPORATION OF THE DISTRICT OF o ELECTEOMEGNET Eon TELEGnArHoNEs Patented Oct. 6, 1908.

- To all whom 'it may concern: V v

Be it known thatwe, PEDER OLUF PEDEE- sEN and VALDEMAR PoULsEN, subjects of the King of Denmark, 'residing at .Vestervoldgade 2, Copenhagen, Denmark, have invented certain new and useful Improvements inA Electromagnets for Telegraphones, of which cuit. The iron. core of the electromagnet isv maintained either in direct4 contact with the record medium2 or in veryintimate proxim` it thereto during the movement or passage o said medium. So far as we are aware, an

' electromagnet having an iron core has always been found necessary inA this class'of apparatus. E

` The present invention comprehends the usemof an electroma et in? the form of a solenoid, through the axis of which the steel body in the formof a wire moves.

The invention is illustratedin. theaccompanying drawing, in which,

Flgure 1 is a conventional sectional'view of a solenoid and recording medium. y Fig. 2 illustrates the path' of lines of force under two different conditions. Fig. 3 illustrates the lines of force emanating from thin and-m thick recording mediums. 4 Fig.' 4 illustrates the relative arrangement v,of a solenoid, recording medium and storingreels for the latter; and Figs. 5 and 6 illustrate two forms of helix wit l electromagnetof the above character, haveiron mantles'for the solenoids.

Attempts, to use a simple solenoidlor wire out any iron core, in place of an not hitherto proved'successful in ractice for v. the followingreason: A solenoi in` a. me-I of uniform magnetic permeability,

v such as air, produces. lines of force extending in continuous curved paths through-the helix in lone direction andl 'around the outside ends.

thereof in thejother direction..l But, .as soon as a body of high permeability, such as iron or steel; 1s introduced into thesolenoid, such body becomes strongly magnetized and d'efv .velops north and'southpoles at its respective In other words, when the core -of the solenoid is straight like an iron bar, it necessouth 'field o ,duced in the iron or steel body from o vor return througli'j.` tant from the sarily develops a north pole at one end and a dpole at the other, end, when mag- But lines of force always start from every north pole and flow as directly as possible toward t e south pole. This condition is illustrated in Fig. 1 of the drawings, where the path; of the lines outside of the core is shown by the dotted lines..` It is evident that these lines of force ilowing from the north toward the south pole, as above described, coincide in direction with the magnetic field of the coil exterior of the latter,

netize lbut oppose the direction of the magnetic The resultthe coil within such coil. ant field within the coil is therefore weaker or less effective than itwould be if not partly neutralized in the above manner. The

roblem therefore consists in causing as force flowing from the north to the south arge as possible a proportion of the lines of pole of the magnetized core to return outside the solenoid where they coincide in direction with the iield of the latter rather than inside Where they o pose its field.

Nowby thoroug study and experiments, we'have ascertained that a solenoid can be employed for telegraphone purposes', and means and ways can be found by which the lines of force are caisedto move in the greatest possible number outside the solenoid. In

. other words, means have been found to prevent the lines of force from the lfree poles prol y posing or neutralizing the lines of force "wit the solenoid due tp its magneto-motive force.

l This being accomplished, it is evident that' an iron or steel body within the solenoid can be strongly -magnetized, and it becomes possibleto use asolenoid fortelegraphone purposes This result issecured by three fac-.- tors as follows:

ings, -where t e dotted lines represent the lines of lforce when the core is .comparatively longwhile the full lines indicate the lines of l force when Ithe core is short. The same ref1. The adjoiningpoles ofthe steel wire I thicker wire.

sult can, of course, be obtained by moving the wire or record medium through the solenoid at greater speed, it being evident that a greater speed of the record medium spaces the magnetic poles which may be developed therein further apart from one another.

2. The record medium must have as small a cross section as possible. The reduction of the diameter or cross section produces, relatively speaking, the same result as increasing the speed; that is to say, it causes the magnetized body within the solenoid to be as relatively long and slender as possible. 'lhe conditions, with a slender record medium and a thick record medium,areindicated at the upper and lower parts of Fig. 3, Where it will be seen that the lines of force are more distant from the thin wire than from the It is also of importance that the turns of the solenoid be kept as lclose as possible to the Wire or record medium, since the more closely the Wires surround the record medium, the more nearly does the exterior field thereof coincide with the lines of force developed from the iron body or core. Moreover, the solenoid is more eflicient in its magnetizing action, or magneto-motive force if it closely. surrounds the core or body to be magnetized.

3. Finally, if a mantle of iron or material more permeable to the lines of force than air, is fixed upon the exterior of the solenoid, a larger number of lines of force will be conducted around the exterior of the coil. This result follows, since placing an iron mantle or the equivalent on the exterior of the solenoid, tends to approach the condition of a complete magnetic circuit of uniform ermeability around and through the so enoid. The more this condition is approached, the less will there be any neutralizing or demagnetizing action' within the solenoid, as above described. With a complete magnetic circuit of uniform permeability throughout, there would be no free poles formed at any point, and substantially no demagnetizing or neutralizing action within the solenoid whatever.

By a suitable combination of the above described three factors, very favorable results can be obtained with the use of solenoid coils. v

Thevessence of the present invention, therefore, consists in providing by suitable means l for a suflicient number of magnetic lines of force passing through the solenoid coil, so as to insure the efficient magnetization of the record medium, and the audible storing up of the conversation to be recorded and reproduced.

In the 'several figures of the drawing, a indicates the record medium and b the solenoid winding.'

For the vrecord medium, a thin steel wire lmay be advantageously used, of the form showiein Fig. 4, which, on account of the small' cross section, not only is of special advantage for the use of solenoid coil for thc above described reasons` but is also very an vantageous in that a thin steel wire can he wound l'roin om` roller c on to anoi her fl, and possesses a very high rotentireness. This is a matter of great importance when it connes to the application ol' the lolcgraphone principle for telephoniey purposes.

i The solenoid coil /i o1' Fig'. l likeuise von sists of very thin line spun copper wire whirh is so wound that between thcsieel wire and the inner wall of the coil only a very sniall -space remains. The coil must not he loo thirh so that a sufficient number of lines ol' l'orre can pass outside around the coil. ll n order lo conduct the lines of force as much as possihli` outwards, around the coil arranged an iron mantle c, (Figs. 5 and G) which to avoid eddy currents is advantageously made in a number of parts. may consist of single bars insulated from one another which can be connected by front plates. The arrangement shown in Fig. o in which wires running radially and connected at the ends are used can be employed to advantage. The choice of the mantle is limited to no definite form; it is only of importance that it fulfils its purpose of guiding the lines of force outwards.

As for the above-mentioned reasons the speed with which the record medium is moved plays a considerable part, it should be mentioned that the less the speed, the thinner must be the steel wire and the smaller the cx terior diameter of the solenoid coil.

Instead of guiding the lines of force outwards by means of an iron mantle surround ing the coils, in certain cases pieces of iron and in other cases 'magnet bodies may be provided at a certain distance outside the coil, as at g Fig. 4, so that they assist to draw the lines of force outwards.

In every case, in order to secure practical results, care must be taken that su'llicient lines of force pass without the solenoid coil.

Whatwe claim, is

1. In telegraphones, the combination of a record medium and a solenoid coil through which the medium passes, said coil being of such dimensions, speed, form and position that an effective number of lines of force take a path outside of the coil, substantially as described.

2. In a telegraphone, the combination of a record medium and a solenoid coil surrounding said medium and through which the medium moves, said coil being of such position, form and construction that lines of magnetic force issuing from the magnctizcd record medium find a path in an effective numberoutside of the coil, substantially as described.

3. In a telegraphone, the combination of a movable record medium, a solenoid coil and an iron mantle surrounding said coil for di- As shown in Fig. 5, the mantle .1

Illlfi llo coil, for the purpose set forth.

'structed ina ltially as descrl recting an 'effective number of lines of vforce outside of the coil.A

4. In a telegraphone, the combination of a record medium, a solenoidc'oil surrounding the samev andl having Van iron mantle conpluality of sections, substanv 5. In a telegraphone, thecombination of a record medium, a solenoid coil surroundingl the same and a body or bodies of magnetic material located outside of the solenoid coil, for the purpose set-forth.

6. In a telegraphone', the combination of a record medium, a solenoid coil'surrounding the same, and magnets located outside of the 7. In a telegralllone, arecord'A medium comprising a steel wire of comparatively great length and small diameter,l a pair of spools from one' to the otherof which said wire is wound and unwound, -a solenoid coil surrounding said Wire and of suiciently small diameter to enable an eiective number of magnetic lines of force emanating from tle'reclord medium to take a path` outside of t e coi 8. In a telegraphone, the'combination of a I record medium, and a solenoid coil through set our hands in the presence of two witnesses.

PEDER- OLUF PEDERSEN. VALDEMAR POULSEN. Witnesses:V

JENs HERMAN CBnIsTENsE, J. C. JAooBsEN.. 

